1. Field of the Invention
The present invention relates to a liquid pressure control device for an automobile load responding brake, which transmits liquid pressure outputted from a master cylinder or the like to a rear wheel brake cylinder by reducing the liquid pressure at a predetermined ratio corresponding to the amount of movable load. More particularly, the invention relates to the improvement of a load sensing mechanism.
2. Description of the Related Art
The liquid pressure control device of the above-noted kind relating to the present invention is disposed halfway in a liquid pressure passage leading from the brake master cylinder to rear wheel brake cylinders. During the application of a low braking force in an initial braking stage, a braking force equal to that applied to a front wheel side is given to a rear wheel side. When the braking force exceeds a predetermined value, the braking force smaller than that applied to the front wheel side is given to the rear wheel side. In this way, rear wheel locking is prevented. In addition, for a vehicle such as a truck or the like, the amount of movable load determines the size of a braking force for causing rear wheel locking. Accordingly, the braking force for starting the reduction of the rear wheel braking force is set larger when the amount of movable load is large. When the amount of movable load is small, a braking force for the same purpose is set smaller.
FIG. 13 illustrates a dual type load responding brake liquid pressure control device denoted by a numeral 101. Valves 105 and 106 are opened/closed respectively by a pair of plungers 103 and 104 which are disposed in a housing 102 so as to be freely slid and respond to loads independently of each other by liquid pressure from a master cylinder or the like (not shown). The liquid pressure from the master cylinder or the like is reduced at a predetermined ratio and then transmitted to left and right rear wheel brake cylinders (not shown).
For providing a characteristic to the valves 105 and 106 according to the movable load amount of a vehicle, a device for increasing rear wheel braking force control starting pressure has been known [as is disclosed in Japanese Utility Model Provisional Publication No. 63-148567 (No. 148567/1988)]. This device increases rear wheel braking force control starting pressure more when the amount of movable load is larger by applying forces to the respective plungers 103 and 104 with a load sensing mechanism 111 according to the amount of movable load and changing the pressure reducing operation starting points (pressure) of the valves 105 and 106.
The load sensing mechanism 111 includes a spring for providing a pressing force according to the movable load amount of the vehicle, one end of the spring being connected to an axle side, a load sensing lever 113, one end of the load sensing lever 113 being supported in the housing 102 of the valves 105 and 106 so as to be swung and the other end thereof being connected to the other end of the spring, an equalizer 114 brought into contact with one end of each of the plungers 103 and 104, and a clamping member 115 for fixing the equalizer 114 at a predetermined position of the load sensing lever 113.
FIG. 14 illustrates a single type load responding brake liquid pressure control device denoted by a numeral 201. A valve is opened/closed by a single plunger 203 which is disposed in a housing 202 so as to be freely slid and responds to a load by liquid pressure from a brake master cylinder or the like. The liquid pressure from the master cylinder or the like is reduced at a predetermined ratio and then transmitted to a rear wheel brake cylinder.
For providing a characteristic to the above-noted valve according to the movable load amount of a vehicle, a device for increasing rear wheel braking force control starting pressure has been known [as is disclosed in Japanese Utility Model Publication No. 3-22055 (No. 22055/1991)]. This device increases rear wheel braking force control starting pressure more when the amount of movable load is larger by applying a force to the single plunger 203 with a load sensing mechanism 211 according to the amount of movable load and changing the pressure reducing operation starting point (pressure) of the valve.
The load sensing mechanism 211 includes a spring for providing a pressing force according to the movable load amount of the vehicle, one end of the spring being connected to an axle side, and a load sensing lever 213 brought into contact with one end of the plunger 203, one end of the load sensing lever 213 being supported in the housing 202 of the valve so as to be swung and the other end thereof being connected to the other end of the spring.
In the liquid pressure control device 101 shown in FIG. 13, the load sensing lever 113 of the load sensing mechanism 111 for applying forces to the plungers 103 and 104 of the valves 105 and 106 according to the amount of movable load and the equalizer 114 provided between the plungers 103 and 104 are brought into point-contact with each other by a projecting section 114a. The equalizer 114 and the plungers 103 and 104 of the valves 105 and 106 are brought into point-contact with each other respectively by projecting sections provided in portions of the equalizer 114 brought into contact with plunger ends 103a and 104a.
However, there is a problem inherent in the liquid pressure control device 101. Specifically, during operation, hitting sounds are produced because of clashing between the load sensing lever 113 and the equalizer 114 or between the equalizer 114 and the plunger ends 103a and 104a. During non-operation, the equalizer 114 is in a free state (there is play). Especially, when the brake is not operated during traveling of the vehicle, the equalizer 114 is vibrated and brought into contact with the load sensing lever 113 or other parts. Consequently, abnormal sounds are produced.
In the single type liquid pressure control device 201 shown in FIG. 14, a stem 214 is fixed in the load sensing lever 213 side of the load sensing mechanism 211 for applying a force to the plunger 203 of the valve according to the amount of movable load. Between the stem 214 and the end of the plunger 203, a cap 216 and a steel ball 217 are disposed in order. The cap 216 is fitted on the stem 214 so as to be slid by interpolating a rubber plate 215 and the steel ball 217 is held in the cap 216. When the brake is operated, even if clashing occurs between the stem 214 and the plunger 203, its impact force is softened or absorbed by the rubber plate 215. Thereby, abnormal sounds are prevented from being produced.
However, there is also a problem inherent in this single type liquid pressure control device 201. Specifically, as described above, an impact force is softened or absorbed by the rubber plate 215 between the load sensing lever 213 and the end of the plunger 203 and thereby the occurrence of abnormal sounds can be prevented. But the rubber plate 215 is not so durable, the structure of the device is made complex and manufacturing costs are increased.